Christian Heresies of the
Fifth Century:

Pelagians:
    Heresy against Man. Pelagius, a "saintly" man according to St. Augustine, claimed that children are born without original sin, as pure as Adam was before he fell; men neither die because Adam fell, nor rise again in consequence of Christ’s resurrection; un-baptized as well as baptized infants are saved; the Mosaic Law is as good a guide to heaven as the Gospel. Condemned at the Council of Ephesus, 431.
    Pelagianism was a heresy altogether different than the other major heresies to occupy religious minds during the time of the late Roman empire. Had previous heresies tried to provide alternative faiths on the holy trinity, then Pelagianism concerned itself with man.
    Pelagianism derives its name from Pelagius who lived in the 5th century A.D. and was a teacher in Rome, though he was British by birth.  It is a heresy dealing with the nature of man.  Pelagius, whose family name was Morgan, taught that people had the ability to fulfill the commands of God by exercising the freedom of human will apart from the grace of God.  He denied original sin, the doctrine that we have inherited a sinful nature from Adam.  He said that Adam only hurt himself when he fell and all of his descendents were not affected by Adam's sin.  Pelagius taught that a person is born with the same purity and moral abilities as Adam was when he was first made by God.  He taught that people can choose God by the exercise of their free will and rational thought.  God's grace, then, is merely an aid to help individuals come to Him.  
     Pelagianism fails to understand man's nature and weakness.  We are by nature sinners (Eph. 2:3; Psalm 51:5).  We all have sinned because sin entered the world through Adam:  "Therefore, just as sin entered the world through one man, and death through sin, and in this way death came to all men, because all sinned" (Rom. 5:12, NIV).  Therefore, we are unable to do God's will (Rom. 6:16; 7:14).  We were affected by the fall of Adam, contrary to what Pelagius taught.
    To what extent the heresy survived is not documented. Though one can surely state that Pelagianism is still with us today. Most Christian parents would struggle to see their new born infant as anything but innocent, and few of them would think they did not possess the free will.
     Pelagius was condemned by the Ecumenical Council of Ephesus and excommunicated in 417 A.D. by Pope Innocent I.
   Little is known about Pelagius. He is spoken of by several of his contemporaries as a Briton. In 409, to avoid Alaric’s siege of Rome, he escaped with his convert and pupil, Caelestius, to Northern Africa, and had gone from there to Palestine before the meeting of the Council of Carthage in 411, which condemned Caelestius. Pelagius is not heard of after 418, but there is a tradition that he was 70 years of age when he died in some obscure town in Palestine. He appears to have been a very good man (St. Augustin called him "saintly") , of more than common moral strictness and purity, if not a man of any great spiritual depth or intellectual grasp. He fell into heresy through contact with a Syrian priest named Rufinus; not, however Rufinus of Aquilea who disputed with St. Jerome. Pelagianism  Heresies Catholic Apologetics  

Semipelagians:
    Errors: Some are predestined to heaven, other to hell. The beginning faith depends on man’s free-will, while faith itself and its increase depend absolutely upon God; nature has a certain claim to grace; final perseverance is not a special gift of grace but depends upon man’s own strength; some children die before baptism, and others after on account of the foreknowledge God possesses of the good or evil they would have done if they had lived.
    Traced to John Cassianus, Abbot of the Monastery of St. Victor, a celebrated and holy man, who, although never formally canonized, was venerated as a Saint, and whose name appears as such on the Greek Calendar. He was the first to introduce the rules of Eastern monasticism into the West. Being the son of wealthy parents, he received a good education. He first entered a monastery in Bethlehem but later withdrew into the Egyptian desert, being attracted by the holiness of the hermits there. During a visit to Rome he was elevated to the priesthood, and subsequently founded two monasteries at Marseilles, one of which he ruled as Abbot.
    The errors of the Semipelagians were condemned in the year 432 by Pope Celestine I; in 529 by Pope Felix IV, in the Synod of Orange and the Synod of Valence, both of which Councils were confirmed by Pope Boniface II.

Nestorians:
    Nestorius, a good monk, taught that there were two separate persons in Christ, one divine and the other human; and claimed that Mary was the mother of the human person only, not of the divine, not the Mother of God. Condemned at the Council of Ephesus in 431.
    Nestorianism is the error that Jesus is two distinct persons.  The heresy is named after Nestorius, who was born in Syria and died in 451 AD, who advocated this doctrine.  Nestorius was a monk who became the Patriarch of Constantinople and he repudiated the Marian title "Mother of God."  He held that Mary was the mother of Christ only in respect to His humanity.  The council of Ephesus was convened in 431 to address the issue and pronounced that Jesus was one person in two distinct and inseparable natures:  divine and human. 
      Nestorius was deposed as Patriarch and sent to Antioch, then Arabia, and then Egypt.  Nestorianism survived until around 1300.
      The problem with Nestorianism is that it threatens the atonement.  If Jesus is two persons, then which one died on the cross?  If it was the "human person" then the atonement is not of divine quality and thereby insufficient to cleanse us of our sins. Nestorianism

Predestinarians: Lucile, a priest, taught that God absolutely and positively predestined some to eternal death and others to eternal life, in such a manner that the latter have not to do anything in order to secure salvation; that Christ did not die for the non-elect, since they are destined for hell. Condemned in 475 in the Council of Lyons. This error will be taught by Calvin, Jansenius, Universalists, Arminians and others.
    Predestination is a hot topic, but the truth is that God knows everything, present, past and future... He knows already if you and I are going to Heaven or to Hell, but He does not predestine it, your salvation and mine depend on the grace of God and our free will, our acceptance of His grace or rejection of it... we are Free, like God, and the fact that God already knows, it does not take away our freedom, our free will. Predestination, Catholic    Predestination, Protestant   Predestination, general religions

Monophysites:
    Eutyches, an abbot of 300 monks, proclaimed the Jesus had only one nature: divine, He is God but not man. Condemned excommunicated in the 6th century and in the Council of Constantinople in the year 680.
    Monophysitism is an error concerning the nature of Christ that asserts Jesus had only one nature, not two as is taught in the correct doctrine of the hypostatic union:  Jesus is both God and man in one person.  In monophysitism, the single nature was divine, not human.  It is sometimes referred to as Eutychianism, after Eutyches 378-452, but there are slight differences.  Monophysitism arose out of a reaction against Nestorianism which taught Jesus was two distinct persons instead of one.  Its roots can even be traced back to Apollinarianism which taught that the divine nature of Christ overtook and replaced the human one.
      Monophysitism was confined mainly to the Eastern church and had little influence in the West.  In 451, the Council of Chalcedon attempted to establish a common ground between the monophysitists and the orthodox, but it did not work and divisions arose in the Eastern church which eventually excommunicated the monophysitists in the 6th century.  
       The denial of the human nature of Christ is a denial of the true incarnation of the Word as a man.  Without a true incarnation there can be no atonement of sin for mankind since it was not then a true man who died for our sins.  
      It was condemned as heresy at the Sixth Ecumenical Council in 680-681. Monophysitism